How many integers 100>n>10 are such that, if the digits of n are reversed, the resulting integer is n+9?
i am probably wrong but i'll take a shot at it:
i get 8 but only by logical thinking (no formulas)
12, 23, 34, 45, 56, 67, 78, 89
in order for it to be n+9, the units and tens digit has be be consecutive (since n + 10 would just be a change in the tens digit 10x)